In the remainder of the present document, a set of emitting/receiving devices in such a network or system share the same transmission channel to communicate with one another. These devices are divided into two groups: a first group constituting a central point and a second group consisting of users. In such systems, all emitting/receiving devices of the central point receive data signals sent by all user emitting/receiving devices and vice-versa, even if those signals are not intended for them. To identify the various data signals received by a emitting/receiving device it is necessary to separate them, for example in order to determine the response of the transmission channel set up between first and second emitting/receiving devices. The response of the channel is a function representing the attenuation of the channel, for example. Access networks and local area networks are examples of such networks.
In a system such as that described above, in the downlink direction, the emitting/receiving device of a given end user receives all data signals sent by one or more emitting/receiving devices of a central node even if only one of those data signals is in fact intended for it. Similarly, in the uplink direction, a emitting/receiving device at the central node receives all data signals sent by one or more of the end user emitting/receiving devices.
A consequence of this is that the data signal received by the emitting/receiving device of an end user contains not only the data signal intended for them but also data signals sent in the same direction by other emitting/receiving devices of the central node, attenuated to a greater or lesser degree, but nevertheless perceptible, according to whether communication between the various emitting/receiving devices is by wire or wireless, e.g. radio communication. These unwanted data signals cause interference that disrupts reception of the data signal intended for the emitting/receiving device.
To correct the effects of such interference, it is necessary to know the response of the various channels of the system in the frequency or time domain.
However, it is difficult to obtain this data, especially when installing a new link or eliminating an existing link or when reinitializing the system. This difficulty stems from the fact that each emitting/receiving device at the central node and each end user emitting/receiving device receives a plurality of data signals.
It is then difficult to know the frequency response of the new link, for example, because it is impossible to identify the data signal conveyed by the new link among the plurality of data signals received.
The paper entitled “Blind Channel Identification and Equalization in OFDM-Based Multiantenna Systems”, Bölcskei et al., IEEE Transactions on Signal Processing Vol. 50, No. 1, Jan. 2002, describes a method of separating data signals conveyed by the various links constituting the system. Such a method is executed in two stages: in a first stage in a emitting/receiving device acting as sender and in a second stage in a emitting/receiving device acting as receiver. This method is a blind identification method.
To separate the received data signals and thereby identify the various links constituting the system, the method described in the above paper modifies the cyclostationary periodicity of the data signals conveyed by the links of the system.
Such a blind identification method applies a precoding algorithm to the data to be sent the function of which is to modify the cyclostationary periodicity of the data signals. The precoding sequences applied to the data to be sent are different for each data signal. Thus after sending it each data signal has its own cyclostationary periodicity.
The various data signals are separated in the emitting/receiving device acting as receiver by applying a cyclic autocorrelation function. Such a function is a second order statistical function that when applied to one or more data signals causes source effects to occur that are linked to the cyclostationary periodicity of the data signals to which it is applied. By modifying the cyclostationary periodicity of the data signals, the occurrence of these source effects is controlled and it becomes possible to separate the various data signals received by a emitting/receiving device.
Although enabling efficient separation of the various data signals received, such a blind identification method has the drawback of being costly to implement.
This method requires the use of means for generating precoding sequences to be applied to the various data signals. Generating these precoding sequences requires a greater computation power and a greater storage capacity, a consequence of which is modification of the structure of the emitting/receiving devices acting as senders of the data signals. Moreover, such a method introduces a modification of the structure of the data linked to the application of the precoding sequences to the data. This modification of the structure of the data also leads to modification of the emitting/receiving device acting as receiver, which must be capable of decoding the received data in order to use it.
All these modifications lead to an increase in the cost of the equipment installed in the telecommunications network. There is therefore a need for a solution that separates the various data signals received by the same emitting/receiving device in order to correct effects linked to the phenomenon of interference and does not lead to any increase in the cost of the network equipment.